The OSHA standard for control of exposure to inorganic lead is 50 Mug/m3 measured by total mass sampling. In setting the standard, OSHA assumed arbitrarily a constant value of 12.5 Mug/m3 as the amount of particulate less than 1Mu in size in any airborne sample, no matter what the source of total airborne concentration. This particle size distribution was then used to model the blood level distribution as a function of airborne lead concentration. The underlying hypothesis in this proposal is that the percentage of lead particulate less than 1Mu in any sample is not fixed but varies according to the source of exposure, the aerosol generating process, and the resulting relationship between the percentage of small lead particulate and total airborne lead concentration. The particle size distribution is therefore determined by the source and conditions of exposure. If our hypothesis is borne out the OSHA PEL may be underprotective or overprotective depending on the source of lead aerosol generation. The overall goal of the proposed research is to assess whether a lead PEL based on respirable sampling or respirable plus total mass sampling represents a more meaningful estimate of exposure. This would be accomplished by studying the impact of a variety of size distributions of lead aerosol in the predicted distribution of blood lead levels in workers exposed to airborne lead. The specific objectives are: 1. Determine the particle size distribution of lead aerosol by cascade impactor in selected industrial processes selected to represent a range of distributions of particle size. This will be done using both stationary samples to characterize the process and personal samples to assess variability because of worker movement. 2. Model the distribution of blood lead values using each of the lead aerosol size distributions and the Bernard model for lead absorption, distribution and excretion. 3. Characterize the magnitude of the differences in predicting blood lead distribution using the current OSHA total mass based method and a method which would differentiate respirable and nonrespirable lead. Size sampling will be carried out in a brass-bronze foundry, secondary smelter and battery manufacturing plant using personal cascade impactors for both area and personal sampling. This research may enable the development of a lead exposure sampling scheme whose end result is better protection for lead exposed workers.